Enum DmaPassthrough 

pub enum DmaPassthrough<'a> {
    Allowed,
    SoftwareBlocked,
    HardwareNestable(&'a (dyn Any + Send + Sync)),
}

How a device’s DMA relates to host passthrough (VFIO assignment).

This is the only IOMMU-related view exposed to consumers of DmaTarget. It deliberately says nothing about how guest memory is translated (that is the underlying DmaTargetIommu factory); it only answers “can this device be handed to the host for passthrough, and if so, how does the assignment backend attach to the IOMMU?”.

Variants

Allowed

No IOMMU, or none relevant to passthrough — host assignment allowed.

SoftwareBlocked

Behind a software/emulated IOMMU that cannot program the host IOMMU for passthrough DMA — host assignment rejected.

HardwareNestable(&'a (dyn Any + Send + Sync))

Behind a hardware-nestable IOMMU — host assignment allowed. The opaque handle lets the assignment backend (which knows the concrete IOMMU type) downcast and attach to the emulated IOMMU for nested stage-1 translation.